NEW YORK, Aug 8 (Reuters) - Schering-Plough Corp. said on Wednesday it won regulatory approval to sell two of its hepatitis C drugs in a combination package that's expected to become the new ``gold standard'' of treatment for a disease that affects 4 million Americans.

The U.S. Food and Drug Administration said the Kenilworth, New Jersey-based pharmaceuticals company can sell Peg-Intron, a longer-lasting form of its Intron A drug, in a single-package combination with its Rebetol drug, also known as ribavirin.

The decision follows an FDA ruling last month granting Schering-Plough the right to sell Rebetol as an individual product. Previously it could only be sold with Intron A. The approval allowed doctors for the first time to mix and match hepatitis C therapies.

The latest FDA ruling enables Schering-Plough to create a single, branded package combining Rebetol and Peg-Intron, for which doctors can write a single prescription.

``This approval allows Schering-Plough to control the process and directly market the combination product,'' said Steven Tighe, an analyst at Merrill Lynch & Co.

Schering said both Rebetol and Peg-Intron will be available separately on the market this fall. At that point doctors will be able to combine them. The company declined to articulate, however, its marketing plans for the combination package.

The approval gives Schering-Plough a jump on Swiss rival Roche Holding Ltd. , which has developed a competitor to Peg-Intron called Pegasys. Roche is expecting the FDA to approve Pegasys in the U.S. by early next year.

While doctors will be free to prescribe Rebetol with either Pegasys or Peg-Intron, analysts expect most doctors will prescribe Schering-Plough's combination, partly because of the convenience and partly because of the direct marketing clout Schering-Plough will be able to bring to the table in selling the drug package to physicians.

Sanford Bernstein analyst Richard Evans predicts that sales of Schering-Plough's hepatitis C drugs in the U.S. will double next year to $1.4 billion from $700 million this year. He predicts global sales will rise 56 percent to $2.5 billion from $1.6 billion.

Peg-Intron uses proprietary technology developed by Enzon Inc. Under the company's agreement with Schering-Plough, Enzon is entitled to royalties on worldwide sales of Peg-Intron. Schering-Plough licenses ribavirin from ICN Pharmaceuticals Inc of Costa Mesa, California.

Schering-Plough's shares rose 17 cents, or 0.45 percent, to close at $38.35 on the New York Stock Exchange. Enzon's shares rose $4.85, or 8.07 percent, to $64.96 on Nasdaq. ICN's shares fell 13 cents, or 0.39 percent, to $32.85 on the New York exchange.